Engine
Reconditioning Overview & Tips
For your 1929-1955 Chevrolet Straight Six Engine
December
02, 2001
Edited
by: James W. Burnes
Part
III: CYLINDER BLOCK & ROD/PISTON ASSEMBLY
The
cylinder block is a one-piece casting. On the left side and rear
are cut-type core plugs. To replace these: drive the sharp corner
of a chisel into the center of plug and pry out. Clean the seat,
and for extra precaution, apply a non-drying sealer such as Permatex
to the seat. Drive new plug into place.
The
Cylinders
Maximum
permissible out-of-round is .002 inch and taper of cylinder walls
should not exceed .005 inch. The photo at right (A1) shows the
method of measuring the cylinder. Before removing piston and rod
assemblies be -sure to cut away the ridge at top of cylinder to
prevent damage to piston ring lands. If new rings are to be installed
in worn cylinders, remove the glaze with a hone. If one is not
available, use a medium grade of emery paper and work it around
the area of ring travel in an oscillating motion to duplicate
a honed finish. This procedure will decrease ring break-in time.
Connecting
Rods and Piston Assembly
Connecting
rods and pistons are removed from the top of the cylinder after
head and oil pan are removed. The rod nuts are locked in place
by stamped metal Pal-Nuts. These Pal-Nuts are turned on rod bolt
by hand after rod nuts have been tightened to correct torque,
then they are given one-quarter turn with a wrench which is sufficient
to lock them. If rod cap sticks in place after removal of rod
nuts, tap side of rod and cap with soft hammer, pulling on cap
at same time. This should release cap. Note the position of rod
oil dippers at this time; also note whether both rod and cap are
numbered for their respective cylinder.
Caution:
Note number of shims in place between rod and cap and reassemble
in same manner if no bearing adjustment is to be made. If pistons
are to be used again, be sure to remove ridge at top of cylinder
before taking out pistons. This is to prevent damaging the piston
ring lands.
Piston
pin is locked in the piston and rod assembly by a cap screw in
the rod. A tab type lock washer is used under the head of this
cap screw and should always be replaced by a new one whenever
disturbed. The cap screw should be tightened to a torque of 25
- 35 pounds foot while piston is clamped in a piston vise (an
alternate method is to clamp a piece of bar stock [of smaller
diameter than the I.D. of piston pin] in a bench vise, slip piston
assembly on the bar and tighten to specified torque. Then lock
tab washer.)
When
reinstalling piston and rod assembly, use a ring compressing tool
to prevent breakage of rings and ring lands. Install assembly
so that top of piston is flush with top of cylinder, then pull
the connecting rod onto the crankpin. Do not tap the assembly
into place from above as rod may be slightly out of line and damage
to crankpin or bearing may result. Be sure rod cap seats tightly
against rod fork ( with correct number of shims in place ) without
bind and that cap is not on backwards before installing oil dipper
and rod nuts.
After
rod nuts are tightened, check for side play of the rods. If rods
do not have the specified movement sideways on the crankpin (0.004
- 0.012 inch), there is either too little bearing clearance. rod
cap is on backwards, burrs on the side of rod bearing surface
or the rod is misaligned. Do not complete engine assembly until
the cause of this trouble is located.
Questions
or comments?
E-mail the editors!
Read
Part I, overview of the straight six engine
Read
Part II, engine removal and reinstallation
Read
Part III, cylinder block and rod/piston assembly
